Clinical History

A previously healthy 40-year-old man arrived in the emergency department after a fall while running at the park, complaining of left flank pain.His vital signs were within normal limits and remained stable; the results of his physical examination were normal. Blood tests were within normal range (Haemoglobin: 15.1 g/dL).

Discussion

Simple, urine-filled cysts are the most common space-occupying lesions of the kidney, with a highly variable reported prevalence range, from 5 to 41% [1]. Simple cysts are generally asymptomatic, representing an incidental finding on abdominal examinations. Complications are rare [1], represented by haemorrhage, infection or rupture, spontaneous or post-traumatic. Only few cases of post-traumatic cyst rupture have been described in the literature [2-6]. Usual manifestations of cyst rupture include flank pain, as in our case, haematuria, flank swelling, ecchymoses. Acute anaemization is usually present.X-ray and US examination are often the first imaging examination for patients complaining of left flank pain after a minor trauma in order to exclude fractures and identify splenic injury. CT scan is usually performed in patients with drug-resistant pain or in case of uncertain ultrasound diagnosis; in our case CT was used to clear up the diagnosis and evaluate the presence of active bleeding.Simple cysts are oval or circular-shaped lesions with a sharply defined outline and a smooth thin wall, avascular, homogenously anechoic on US examination and with a radiodensity similar to water on CT. In case of acute haemorrhage there is an increase of the attenuation value of the intracystic content (70-90 Hounsfield Unit), then, as blood liquefies and organizes, the attenuation values tend to decrease. In our case we observed an intracystic haemorrhage, a perirenal haematoma and a retroperitoneum haemorrhage.CT allows a quick differential diagnosis and identifies the source of bleeding. In our case the integrity of the spleen was shown by US and the cause of the bleeding was clearly a renal mass, excluding the adrenal aetiology. According to the hypodensity of the lesion in absence of fat components or vascularization we confirmed that the bleeding was related to the rupture of a renal cyst.In case of rupture of a renal cysts, a conservative approach with supportive treatment and blood transfusions may be sufficient in patients with stable haemodynamic conditions. Arterial active bleeding lesions can be treated surgically or with angiographic embolization.The acute bleeding was treated with embolisation. Imaging follow-up was negative for contrast medium extravasation.Even in case of minor trauma the possibility of retroperitoneal haematoma should be kept in mind.Multiphasic CT is the gold standard for the diagnosis of retroperitoneal haematoma and for the identification of its causes.CT signs of active bleeding change the patient management.

Coils positioned in the embolization (blue arrows). The known cyst presents inhomogeneous density (orange arrows), but no changes in density are recognizable after contrast medium administration (Figure b). No contrast medium extravasation is recognizable.